Type: CMD, from the results, right click CMD
Click 'Run as Administrator'
At the Command Prompt, type: sfc/scannow
This will check for any integrity violations
Restart your system
If the problem continues to persist:
1. Insert the Windows 7 DVD
2. Restart your computer
3. When asked if you want to boot from your DVD drive, do so.
4. Choose your language, click Next.
5. Click 'Repair your computer'
6. Select operating system you want to repair.